1. Field of the Invention
The present invention relates to an image forming apparatus.
2. Description of Related Art
Recently, an image forming apparatus having two developing rollers in a developing area so as to keep good developing performance is proposed along with faster image forming processing. Here, the developing performance means performance to develop right amount of toner and to avoid bad image forming occurred by fog of background density, beads carry over or the like.
If the two developing rollers are arranged in the developing area, a developer flows through a flow path, which goes in a single direction through a supplying section for supplying the developer, a regulating section for regulating flow rate of the developer, first and second developing rollers each for developing toner image to a latent image carrier, and a retrieve section for retrieving developer remained on the second developing roller after a development.
Here, the regulating section is generally located not adjacent to the second developing roller to which the developer is supplied from the first developing roller but adjacent to the first developing roller. That is because, if two regulating sections are respectively arranged adjacent to the first and second developing rollers, such problems may occur that a developing apparatus significantly grows in size or deterioration of the developer may be accelerated.
For the first developing roller, locating the regulating section has a merit that the toner adhered on a surface of the first developing roller is removed. To put it concretely, the remaining toner on a sleeve, which is rotatably arranged on a surface of the first developing roller, is removed by a developer chamber, which is formed by the regulating section and scrapes against the sleeve.
On the other hand, toner pollution occurs on a sleeve of the second developing roller for the reason that a developer chamber is not formed because the regulating section is not located adjacent to the second developing roller. Progression of the toner pollution causes bad image forming such as color cast in a foundation or decrease in concentration, which finally leads to reduction of the developing performance.
For the image forming apparatus having two developing rollers, how to resolve the toner pollution on the sleeve of the second developing roller is a problem to keep good developing performance.
Japanese Patent Application Laid-Open publication No. 2006-139227 discloses a technique for electrically displacing the toner adhered on the sleeve of the second developing roller to the latent image carrier or to the first developing roller in a toner removing mode.
Moreover, Japanese Patent Application Laid-Open publication No. 10-312110 discloses a technique for electrically flying the toner adhered on the sleeve of a developing roller to a conductive roller and removing the toner on the conductive roller by a blade.
However, the technique disclosed in Japanese Patent Application Laid-Open Publication No. 2006-139227 cannot remove the tanner adhered on the sleeve of the second developing roller without being shifted to a particular mode such as the toner removing mode.
Moreover, in the technique disclosed in Japanese Patent Application Laid-Open Publication No. 10-312110, removal effect gradually deteriorates because making the blade to be contacted with the conductive roller leads the toner adhered on the conductive roller.